Now: Let Jenny be "x", then Matthew is "3x".
In 7 years, Matthew will be 3x + 7, and Jenny is x + 7.
Matthew is twice as old as Jenny, therefore
`3x + 7 = 2(x + 7)`
`3x + 7 = 2x + 14`
`x + 7 =...
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Now: Let Jenny be "x", then Matthew is "3x".
In 7 years, Matthew will be 3x + 7, and Jenny is x + 7.
Matthew is twice as old as Jenny, therefore
`3x + 7 = 2(x + 7)`
`3x + 7 = 2x + 14`
`x + 7 = 14`
`x = 7`
Jenny is 7 years old now.
Check:
Now: Jenny is 7, which makes Matthew 21, 3 times as old.
In 7 years, Jenny will be 14 and Matthew will be 28, which is twice as old.